staging: ste_rmi4: Suppress 'ignoring return value of ‘regulator_enable()' warning

drivers/staging/ste_rmi4/synaptics_i2c_rmi4.c:
        In function ‘synaptics_rmi4_resume’:
drivers/staging/ste_rmi4/synaptics_i2c_rmi4.c:1090:18:
        warning: ignoring return value of ‘regulator_enable’, declared
        with attribute warn_unused_result [-Wunused-result

Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: devel@driverdev.osuosl.org
Acked-by: Srinidhi Kasagar <srinidhi.kasagar@stericsson.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>